Elastomeric seal for rotating heads

ABSTRACT

An all-elastomeric sealing element for a rotating control device includes a base portion, a conical portion and has a central pipe opening through both the base portion and the conical section. The conical section has an elastomeric core layer and an elastomeric surface sealing layer which encases the core layer. The surface sealing layer is softer than the core layer, as measured on a standard durometer scale.

FIELD OF THE INVENTION

The present invention relates to an elastomeric sealing element forrotating control devices.

BACKGROUND

Rotating control devices (RCDs) are used to isolate the annulus, containannular fluids under pressure, and divert returns to pressure controland fluid management systems. RCDs connect to the top of the blowoutpreventer (BOP) in the wellhead, and allow rotary drilling and strippingout of a well with positive annular pressure. All RCDs include a sealingelement which forms either a passive or active pressure seal around thedrill pipe. The RCD is an important element in every managed pressuredrilling and underbalanced drilling operation because neitherapplication is possible without one.

The seal element must be flexible enough to allow pipe joints to passthrough the RCD while maintaining a seal around the drill pipe.Conventionally, elastomeric seals such as rubber or polyurethane sealsare used, which provide the needed flexibility. The seals conventionallyhave a steel core or frame which provides strength and rigidity.

Improvements in sealing performance will improve the function of RCDs,such as when used in managed pressure and underbalanced drilling.

SUMMARY OF THE INVENTION

The present invention relates to a sealing element for a rotatingcontrol device. In one aspect, the invention may comprise an elastomericseal, said seal comprising a base portion, a conical portion anddefining a central pipe opening through both the base portion and theconical section, wherein the conical section comprises an elastomericcore layer and an elastomeric surface sealing layer which encases thecore layer, and wherein the surface sealing layer is softer than thecore layer, as measured on a standard durometer scale.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like elements are assigned like reference numerals. Thedrawings are not necessarily to scale, with the emphasis instead placedupon the principles of the present invention. Additionally, each of theembodiments depicted are but one of a number of possible arrangementsutilizing the fundamental concepts of the present invention. Thedrawings are briefly described as follows:

FIG. 1 (prior art) shows a rotating head in cross section with a priorart seal (S) in place.

FIG. 2 shows one embodiment of a seal of the present invention, showingthe outer sealing layer in phantom, and the core layer.

FIG. 3 shows a side elevation view of the surface sealing layer and thecore layer.

FIG. 4 shows a cross section of the seal through the length of thefinger projections.

FIG. 5 shows a cross section of the seal though the gap separating twoadjacent finger projections.

FIGS. 6A-6G show various views of one embodiment of a core layer,showing various dimensions, and are substantially to scale.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention relates to an elastomeric seal for a rotatingcontrol device. Any term or expression not expressly defined hereinshall have its commonly accepted definition understood by those skilledin the art. To the extent that the following description is of aspecific embodiment or a particular use of the invention, it is intendedto be illustrative only, and not limiting of the claimed invention. Thefollowing description is intended to cover all alternatives,modifications and equivalents that are included in the spirit and scopeof the invention, as defined in the appended claims.

FIG. 1 shows a prior art seal (S) installed into a Schlumberger EnsealOptimal™ rotating head. The steel core (C) which is ubiquitous in priorart seals is shown. It may be seen that the steel core (C) does notextend very far along the length of the seal, and steel is of course anon-elastic material. The all-elastomeric seals of the present inventionmay be configured to replace existing seals on any configuration of arotating head from any manufacturer.

As used herein, an “elastomer” is a material which has the property ofelasticity. Elastomers typically have low Young's modulus and high yieldstrain. Elastomers may include saturated and unsaturated rubber, andthermoplastic elastomers. Thermoplastic elastomers may include styrenicblock copolymers, polyolefins, polyurethanes, polyesters and polyamides.

In one embodiment, the elastomeric seal is configured to providereasonable flexibility and sealing ability by a combination of differentelastomeric layers having differing hardnesses. In one embodiment, acore layer is provided which provides strength and rigidity to the seal,but which is itself elastic. Preferably, but not essentially, the corelayer is configured with finger portions to provide rigidity andstrength, while retaining flexibility. The core layer is covered by asofter elastomer, which provides the flexibility essential for goodsealing performance.

An exemplary seal (10) is comprised of an elastomeric core (12) encasedin a surface sealing layer (14). The sealing layer (14) is formed froman elastomeric material which is softer than the core (12) material. Inone embodiment, the core material has a hardness of between about 60 to90 on the Shore D durometer scale, preferably in the range of about 70to 80. In one embodiment, the core material has a hardness of about 75on the Shore D scale. The sealing layer may be formed of an elastomericmaterial having a hardness of between about 60 to 100 on the Shore Adurometer scale, preferably between about 70 to about 90, morepreferably between about 75 to about 85. In one exemplary embodiment,the sealing layer has a hardness of 82 Shore A.

There are known empirical and semi-empirical relationships between Shorehardness and Young's modulus. In one embodiment, the hardness of thecomponents of the present invention may be expressed in terms of Young'smodulus, having regard to any known formula equating Shore hardness andYoung's modulus in MPa.

The core layer (12) provides some rigidity and strength to the seal,while the softer surface layer improves the sealing ability withoutsacrificing too much strength. In one embodiment, the core layercomprises polyurethane having a Shore D hardness of about 75. In oneembodiment, the surface sealing layer comprises polyurethane having aShore A hardness of about 82. Preferably the sealing layer (14) isformed of a material having a relatively low coefficient of frictionwith pipe, which will facilitate the passage of pipe through the seal inoperation. The surface sealing layer may be cast to encase the corelayer, using conventional polyurethane casting methods.

The seal (10) comprises a substantially conical shape in its undeformedstate, having a base portion (20), an inner sealing surface (22) whichis substantially cylindrical, and an outer surface (24). The upper areaof the inner sealing surface is preferably beveled, creating a conicalinner surface (23), to facilitate entry of larger diameter portions ofthe pipe string. As will be appreciated by those skilled in the art,fluid pressure will act on the outer surface (24), causing the innersealing surface (22) to press against the pipe and create an effectiveseal. When a pipe joint passes through the seal, the seal must expand toaccommodate the larger diameter of the pipe joint, but retain itsintimate contact with the pipe in order to maintain the seal.

The base portion (20) is preferably integral with the core layer (12)and formed of the same relatively harder material. The base portioncomprises a flange (21) defining mounting holes (26) for bolting theseal into position. In one embodiment, the conical portion (30) of thecore comprises a plurality of separate finger portions (32) separated byrelatively narrow gaps. In alternative embodiments, the core layer maybe unitary, without finger-like projections. In one embodiment, thenumber of finger portions may vary between about 2 to about 12 or more.In one specific embodiment, the core comprises 10 finger portions (32),equally spaced with uniform narrow gaps, as is shown in the Figures.

In use, the core layer (12) imparts some rigidity to the conical portionof the seal, and improves the sealing performance of the inner sealingsurface by resisting deformation of the seal, because the core layer isformed from a relatively harder material. At the same time, because thecore layer is elastomeric, the conical portion of the seal can stillexpand, allowing the larger diameter of pipe joints to pass through. Inthe example where the core layer comprises finger portions,expandability may be enhanced by ability of the fingers to spread apart.

As may be appreciated by those skilled in the art, the expandability ofthe conical section is dependent on the relative thickness andelasticity of the core layer compared to the sealing layer. As well, thevarious dimensions of the core layer relative to the seal itself, suchas length of the finger portions relative to the length of the conicalsection, as well as the width of the finger projections, and the size ofthe gaps between the finger projections, are also factors. In oneembodiment, the finger portions extend approximately ¾ the length of theconical section of the seal. These parameters may be varied by thoseskilled in the art to achieve different objectives of the seal and itsintended use. An exemplary embodiment of the core layer is shown inFIGS. 6A to 6G, which includes dimensions and is substantially to scale.

In one embodiment, the core layer defines a plurality of openings. Whenthe softer surface sealing layer material is cast around the core layer,the softer material fills the openings, and locks the two layerstogether. In one embodiment, where the core layer comprises multiplefinger portions, each finger may define at least one opening, as isshown in the Figures.

1. An elastomeric seal for a rotating control device, said sealcomprising a base portion, a conical portion and defining a central pipeopening through both the base portion and the conical section, whereinthe conical section comprises an elastomeric core layer and anelastomeric surface sealing layer which encases the core layer, whereinthe surface sealing layer is softer than the core layer.
 2. Theelastomeric seal of claim 1 wherein the core layer comprises apolyurethane having a hardness of between about 60 to about 90 on theShore D durometer scale.
 3. The elastomeric seal of claim 2 wherein thecore layer polyurethane has a hardness of between about 70 to 80 on theShore D durometer scale.
 4. The elastomeric seal of claim 3 wherein thecore layer polyurethane has a hardness aof about 75 on the Shore Ddurometer scale.
 5. The elastomeric seal of one of claims 2 to 4,wherein the sealing layer comprises a polyurethane having a hardness ofbetween about 60 to 100 on the Shore A durometer scale.
 6. Theelastomeric seal of claim 5 wherein the sealing layer polyurethane has ahardness of between about about 70 to about 90 on the Shore A durometerscale.
 7. The elastomeric seal of claim 6 wherein the sealing layerpolyurethane has a hardness of between about 75 to about 85 on the ShoreA durometer scale.
 8. The elastomeric seal of claim 7 wherein thesealing layer polyurethane has a hardness of about 82 on the Shore Adurometer scale.
 9. The elastomeric seal of one of claims 1 to 4,wherein the core layer comprises a plurality of finger portions.
 10. Theelastomeric seal of claim 9 wherein the plurality of finger portionseach define at least one anchor opening through which the sealing layermaterial may set.